The present invention relates to new and useful herbicidal compositions of N-phosphonomethyl-glycine and/or an agriculturally acceptable salt thereof in aqueous solution containing certain herbicidal activity-enhancing nonionic surfactants and a class of foam moderators.
N-Phosphonomethylglycine, also known by its common name glyphosate, and herbicidal salts thereof are highly effective and commercially important herbicides useful in controlling a wide variety of unwanted vegetation. The herbicide is normally applied to the foliage of a very broad spectrum of annual and perennial grasses, broadleaf plants and the like. Once within the plant, the herbicide translocates and is lethal to the whole plant. Usually, glyphosate is formulated in herbicidal compositions in the form of a selected water soluble salt. Commercially, glyphosate in the form of its monoisopropylamine salt is most often sold in concentrated aqueous solution which normally also contains an appreciable amount of a surfactant. The presence of a surfactant provides more efficient utilization of glyphosate and/or its salts dissolved in aqueous solution as compared to like glyphosate-containing solutions to which no surfactant has been added. The more efficient utilization of glyphosate and/or its salts occurs independently of whether the surfactant is anionic, cationic or nonionic.
An undesirable side-effect of the presence of surfactant can be the generation of foam, especially during dilution, mixing and spraying of the herbicide by the user. Alkyl polyglycosides are a class of surfactants useful for enhancing the herbicidal activity of glyphosate formulations but unfortunately have a strong tendency to generate foam which is slow to dissipate.
In European Patent Application 0 220 902 this drawback of alkyl pplyglycoside is not pointedly discussed, but it is suggested that an antifoam agent may be included when an alkyl polyglycoside surfactant is formulated with an aqueous solution of glyphosate. The only antifoam agent suggested in that patent is broadly described as a dimethylpolysiloxane. Most antifoam agents, such as the siloxanes, function by being in a separate phase from the aqueous solution, which allows the antifoam agent to rupture the film surrounding the entrapped air. Thus, in a spray solution, it is desirable that the antifoam agent be insoluble in the aqueous phase of the solution. However, this can have negative effects on the aqueous concentrate solution that is diluted to form the spray solution. It has been found that when silicones, such as the dimethylsiloxanes as suggested in the patent, are used as antifoam agents for aqueous concentrate solutions of glyphosate and an alkyl polyglycoside, a non-homogeneous formulation results upon standing over a relatively short period of time. In other words, there is a pronounced tendency of the silicone to separate from the aqueous concentrate solution as a separate layer. Thus, in such aqueous solutions, the silicone will have to be redispersed before pouring or drawing aliquots of the formulation from its container in order to realize the antifoam properties of the silicone in all aliquots. This redispersion requires agitation, for example, by shaking and stirring. A requirement for shaking or otherwise agitating agricultural chemical formulations prior to use is often ignored by the user, even when clearly advised on the label of the container. When large containers of aqueous concentrate solutions of glyphosate are used, accomplishing the needed agitation may be impractical impossible. Therefore, it is desired in the art to provide an aqueous concentrate formulation of glyphosate containing an alkyl polyglycoside surfactant having an antifoam agent such that the formulation is a homogeneous aqueous concentrate solution where the antifoam agent does not separate with time, yet shows good antifoam properties on dilution with water.
In a publication copyrighted in 1980 by Air Products and Chemicals, Inc. and entitled xe2x80x9cSurfynol(copyright) Surfactantsxe2x80x94Performance in Agricultural Chemicalsxe2x80x9d, it is disclosed that such acetylenic diol surfactants provide beneficial effects in certain agricultural chemical formulations including wetting/surfactant potentiation, antifoam properties, compatibility with other adjuvants and anticorrosion properties. There is no disclosure of using the Surfynol surfactants to moderate the foam problems with aqueous solutions of glyphosate or with any agricultural chemical formulation containing an alkyl polyglycoside surfactant.
In normal agricultural applications, glyphosate is delivered from the herbicide manufacturer to the user in concentrated liquid form. For example, a commercial formulation may contain about 41% monoisopropylammonium glyphosate, as the herbicidally active ingredient, and about 15% surfactant with the remainder water. The glyphosate-containing aqueous solutions are applied at various rates using various application equipment and techniques. Spraying of diluted solutions of the herbicide on the target foliage is often accomplished with aerial broadcast spray, hand-held or boom-mounted applicators which produce a spray of desired force and configuration of active ingredient delivered at a predetermined rate. Spray solutions of the herbicidal compositions may contain from about one-half percent active ingredient to about five percent active ingredient or more to provide a delivery rate to the target plants of about 0.112 kilograms/hectare (kg/ha) to about 11.2 kg/ha. Thus, many commercial formulations of glyphosate and/or its salts require dilution with water. The formulated glyphosate and/or its herbicidal salts mix readily with water. The dilution may be accomplished by filling the mixing or spray tank with the required amount of water and adding the proper amount of formulated glyphosate or salts thereof. The resulting mixture requires agitation, for example, by circulation or agitation stirring. During mixing and application of the herbicidal composition, undesirable formation of foam of the spray solution may occur. While the above-mentioned alkyl polyglycoside surfactant facilitates the efficient use of the activity of the glyphosate and/or salts thereof dissolved in aqueous solution, the use of conventional application techniques is limited because of the foaming problems.
The present invention provides a stable, homogeneous, concentrate formulation of glyphosate and/or its salts, a herbicidally enhancing amount of an alkyl polyglycoside surfactant, and a foam moderating amount of a Surfynol surfactant, that does not foam unacceptably during dilution, mixing, or spraying. This concentrate formulation does not require shaking or stirring before being poured or drawn from the container in which it is supplied, such that each aliquot does not foam unacceptably during dilution, mixing, or spraying. There is no tendency of the Surfynol surfactant to separate from the solution as a separate layer. Upon dilution, the spray solution may be hazy, which indicates that the spray solution is non-homogeneous and at least two phases exist. This haziness is presumably the Surfynol surfactant, which is not soluble in the aqueous phase of the spray solution, which can then function as an antifoam agent in the spray solution. Thus, the glyphosate and/or its salts, alkyl polyglycoside surfactant, and Surfynol surfactant form a homogeneous aqueous concentrate solution, but the spray solution formed upon dilution of the aqueous concentrate solution is non-homogeneous.
There is provided a herbicidal composition comprising an aqueous concentrate homogeneous solution of
a) glyphosate and/or a herbicidal salt thereof in concentrated form;
b) an activity enhancing amount of at least one alkyl polyglycoside surfactant; and
c) a foam moderating amount of at least one acetylenic diol structurally characterized by a symmetrically substituted triple bond and adjacent hydroxyl groups.
Foaming which would normally occur when a diluted aqueous solution of glyphosate and/or its salts is agitated in the presence of an alkyl polyglycoside surfactant is moderated by the use of the composition of the present invention.
The composition in liquid form is prepared by mixing together a glyphosate herbicide, an activity enhancing alkyl polyglycoside surfactant, an acetylenic diol foam moderator, and water to form a homogeneous aqueous concentrate solution wherein the herbicide is present in an amount greater than required for vegetation control. Thereafter, the resulting concentrate solution may be diluted with additional water to adjust the glyphosate concentration to a suitable spray concentration. The resulting diluted solution may be hazy, thereby indicating non-homogeneity. The diluted solution has a reduced foam-forming propensity by comparison with a similar solution lacking the acetylenic diol. The foam more readily dissipates upon standing and forms in lesser amounts when the foam moderating diol is used in accordance with the present invention. The composition of the present invention may be formulated as a powder or granules in which case water will be added later.